1. Field of the Invention
This invention relates to a roll stand assembly as used to form and handle sheet material and, more particularly, to a roll stand assembly having rolls that are relatively repositionable to control gaps between the rolls.
2. Background Art
A myriad of different configurations of roll stand assemblies currently exists for making and handling sheet material. On roll stand assemblies, rolls cooperate to facilitate sheet formation, as by extrusion, and handling of sheets as during treatment, component combination and conveyance. Typically, cooperating rolls will have sheet engaging surfaces, each centered on an axis. The axes of the cooperating rolls are substantially parallel. During sheet formation and handling, a controlled gap is set and maintained, with the gap dimension being determined by the particular process and product. The rolls are relatively repositionable to an “open state” to allow the gaps to be enlarged, as to facilitate access therethrough for assembly, repair, and maintenance of the roll stand assembly.
In certain applications, multiple “nip” locations are formed on the same roll stand assembly where cooperating sheet engaging surfaces converge in a downstream direction. In one exemplary form, one roll will cooperate with two adjacent rolls to produce separate nip locations on the same roll stand assembly. The center roll in this combination is typically capable of moving in a linear path to place the rolls in the aforementioned “open state”, wherein the gaps between the center roll and both adjacent rolls are increased adequately so as to allow access therethrough for repair, maintenance, etc. Preparatory to operation, the center roll is moved oppositely to its opening direction to place the rolls in a “closed” or “operating” state wherein the sheet engaging surface on the center roll is brought into proximity to the sheet engaging surfaces on the adjacent rolls.
The ability to set and maintain a precise gap dimension between roll pairs is dictated by the relative alignment of all three rolls. While generally rolls used in extrusion forming processes are precisely formed, there are nonetheless tolerances that are permitted that often allow for, and result in, a skewing of alignment that produces large forces during operation that may stress system components, cause wear, and potentially contribute to a line breakdown that necessitates system downtime. Roll misalignment may also compromise the product produced using the roll stand assembly.
Heretofore, gap control has been effected principally by controllably moving the center roll in only a linear fashion relative to the adjacent rolls in a multi-nip design. System designers have relied upon the modicum of relative movement between the parts to cause a self-alignment. By doing so, there is a potential for one or more of the rolls to “float” during operation. As a result, the above-mentioned misalignment conditions may occur.
The industry to this point has operated systems with this inherent potential problem, given the fact that no commercially viable solution has been devised.